1. Field of the Invention
The invention relates to a device for transmitting optical signals between units that are rotatable relative to each other, also termed a rotary coupling or rotary joint. With this, a plurality of optical signals are to be transmitted simultaneously along a plurality of channels.
2. Description of the Prior Art
An optical rotary data transmission device for a plurality of channels, comprising a Dove prism, is disclosed in U.S. Pat. No. 5,568,578. For coupling light into or out of glass fibers, an arrangement comprising a plurality of GRIN lenses is provided. The light is refracted at the light entry faces of the Dove prism in accordance with the refractive indices of the glass of the Dove prism and the surroundings. The function of the prism is thus dependent upon the refractive index of a medium surrounding the prism.
An optical rotating data transmitting device for a plurality of channels, comprising a Dove prism as a derotating element, is disclosed in US 2005/0036735. Light from supply light-waveguides is coupled via collimators into a Dove prism to be derotated thereby, and then fed via other collimators into lead-away light-waveguides. In order to make the arrangement independent of the refractive index of a medium in the surroundings of the Dove prism, the prism is provided with supplementary members which ensure a perpendicular light entry. Owing to this perpendicular light entry, no refraction occurs at the interface. A disadvantage of this is a partial reflection of the light from the perpendicular interface, so that at least a part of the light is coupled back into the light guide. This results in a relatively low return loss.
Another kind of optical rotary data transmission device is disclosed in WO 01/98801 A2. Thus, this describes a micro-optical system having optical and mechanical components in the form of a one-piece component part. This design makes it possible to achieve a substantially higher packing density of the individual glass fibers. Once again, the parallel light entry and light exit faces that cause a relatively low return loss are of disadvantage.
A disadvantage of the known prior art is that relatively strong reflections of the transmitted light occur inside the rotating data transmission device.